1. Field of the Invention
The invention relates to a transmission system for sequentially transmitting signal samples, from a transmitter to a receiver. The a transmitter includes characterization means for determining parameters characteristic of the signal samples, and means for transmitting the characteristic parameters and at least some of the signal samples over the channel to a receiver. The receiver includes interpolation means for determining the value of missing signal samples to obtain successive series of signal samples so as having characteristic parameters that correspond to the received characteristic parameters.
In addition, the invention relates to a transmitter, a receiver, a coder and a decoder to be used in such a transmission system, as well as an interpolator and an interpolation method.
2. Description of the Related Art
A transmission system as defined in the opening paragraph is known from U.S. Pat. No. 5,025,404.
Such transmission systems are used, for example, for transferring speech or musical signals over channels having a limited transmission capacity or over channels on which so-called burst errors occur.
A first example of such a channel is a radio channel between a mobile station and a fixed base station. The available transmission capacity of this channel is limited, because it is utilized by a great many users. Besides, there may be periods in which, as a result of fading, the probability of the occurrence of burst errors is rather great.
A second example is a recording channel which utilizes a magnetic, optical or other recording medium such as, for example, a ROM. The capacity thereof is limited, and in some of these recording media burst errors may occur when the recorded samples are reproduced.
In the transmitter the prior-art transmission system, characteristic parameters are determined of the signal samples to be transferred. This may be effected by determining linear prediction parameters which describe the relation between current signal samples and previous signal samples. These parameters are determined in such a way that the error between the current signal sample, estimated on the basis of the previous signal samples, and the actual value of the current signal sample is minimized. The characteristic parameters are transferred to the receiver over the channel together with (a number of) the signal samples.
If a saving on transmission capacity is desired, only some of the signal samples are transferred over the channel. The samples that have not been transferred are then determined at the receiver on the basis of the received characteristic parameters which provide information about the nature of the signal and the samples that have indeed been transferred.
If the signal samples to be transferred are desired to be protected against burst errors, all the signal samples can be transferred besides the characteristic parameters. In the receiver the erroneously received samples are then detected on the basis of the characteristic parameters and the correctly received signal samples. The erroneously received samples are then considered to be missing.
In the transmitter the characteristic parameters are determined which best describe the complete range of signal samples, whereas in the receiver, based on the received characteristic parameters and the values of the (correctly) received signal samples, the values of the missing signal samples are determined. The values of the reconstructed signal samples will generally not be exactly equal to the values of the original signal samples, and so an interpolation error will show up. The missing signal samples are determined such that this interpolation error is minimized.
Simulations have shown that in some speech and musical signals the minimum value of the interpolation error continues to be considerable. In addition, listening tests have proved that the quality of the received signal leaves much to be desired.